Conventional cutting and winding operations for yarn include a doffing/donning operation often performed manually. Typically an operator severs the yarn with scissors while the inlet of a suction or aspirator gun is held against the yarn at a point above the point of severing. Once the yarn is severed, the tail end is wound onto a yarn package while the newly formed leading end is sucked into the aspirator and fed to a waste collector. The suction gun is then placed onto a holder while the yarn package is replaced with an empty tube core. When the empty tube core attains full speed, the operator manipulates the suction gun to attach the yarn to the rotating empty tube core and then severs the yarn again by cutting or tension breaking at the suction gun so that the winding operation may continue. All the yarn going to the suction gun during the transfer time is going to waste.
In order to economize these winding operations, mechanisms which automatically sever, aspirate and rethread the yarn have been developed. U.S. Pat. No. 4,496,109, issued on the application of Cardell, discloses such an auto transfer system where a signal furnished to the machine allows pressurized fluid to be supplied to a hydraulic cylinder. The hydraulic cylinder positions a cutter and yarn aspirator so that yarn enters the cutting slot of a stationary blade adjacent the aspirator. Air is then directed by a cam actuated valve causing pressure to build up in the working compartment of a cutter sleeve. When the pressure eventually overcomes the restraint imposed by a spring ball detent, a reciprocable blade moves forward in a line to surface contact with the stationary blade thereby severing the yarn, the new leading end of which is aspirated to waste. The yarns are then threaded onto new cores, snagged by pinch grooves on the cores, and are broken as the yarn is placed in tension between the aspirator and rotating pinch grooves.
More efficient winders for aramid fibers require auto sever, no waste, transfer devices to sever and transfer the yarn from a full package to an empty tube core rapidly without aspirating any yarn to waste. This invention relates to a no waste transfer system in which a suction gun is not used to capture and transfer the yarn, but rather the yarn is snagged on an empty tube core and instantaneously severed from the full core without wasting any yarn in the process. With some yarns, the tension build-up during snagging is sufficient to break the yarn and accomplish the severing. However for aramid fibers of moderate denier, the yarn is exceptionally strong and does not break except at high force levels. Therefore, an automatic cutting device which is actuated by the tension build-up in the yarn is needed. The cutting device must be very reliable, since if a cut is not completed, the force necessary to break the yarn of higher denier is high enough to damage the winder. An automatic cutting device must also be extremely fast acting so that yarn is cut quickly at the instant of snagging, since aramid yarn has very little elongation under load and the forces build up rapidly. In addition, an automatic cutting device should handle yarns with a wide variety of deniers, since it is most economical to use one cutter for a wide variety of products.